The evermore stringent Environmental Protection Agency (EPA) limitations represented by the Tier 4 reduction of emissions has required significant development in the area of treating the exhaust from the engine to reduce oxides of nitrogen. For internal combustion engines operating on a compression ignition cycle or a homogenous charge compression ignition cycle (HCCI) there is an extra requirement of reducing particulates in the exhaust system so that these particulates are not released to the atmosphere. Such aftertreatment devices require periodic elevation of their temperatures to a point where the carbon particles trapped on the interstices of a particulate filter self combust. Such a process requires additional fuel or other energy form and reduces the efficiency of such an engine system.
In addition to the exhaust aftertreatment of reducing particulates, many current engines use exhaust gas recirculation (EGR) to recycle some of the products of combustion to the intake of the engine to reduce combustion temperatures by virtue of additional quantities of nitrogen. While these systems have been effective in accomplishing this purpose, they are difficult to manage throughout a complex, heavy duty operating cycle. Frequently, such systems require complex control systems whether they be high pressure EGR systems before the turbocharger or low pressure EGR systems, after the turbocharger. Approaches have been used to reduce energy losses by cooling the EGR which adds an additional level of problems to be overcome in terms of acidic condensation in the engine intake.
What is needed therefore is a prime mover system in which energy consumed in which the efficiency of such systems is improved and operating flexibility is achieved.